This invention relates to underground boring devices they may be steered along a chosen path while boring. More specifically, but without limitation, the present invention relates to continuously rotating, steerable, waterjet drillheads located in the forwardly facing end of a hollow, pushed drillstring. The drillhead receives high pressure water from within the drill string and selectively directs, through the appropriate, forwardly facing nozzles, high pressure cutting jets of drilling fluid to cut a curved tunnel that the pushed drillstring will follow. In this way the waterjet drillhead may be continuously steered along a desired path. When installing inground cable, conduit or pipe such as power cables, telephone lines, fiber optic cable, gas lines, water lines or the like the method of trenching is commonly employed. However, when traversing urban areas containing streets, driveways, utilities, buildings and other "obstacles", continuous trenching is sometimes impossible. For military use, it is also desirable to traverse long distances without trenching; for example, when laying a fiber optic cable or pipeline under a beach. It is therefore, highly desirable to have the capability of providing a continuous, underground tunnel for installing cable, conduit, pipe or the like at distances of up to 25,000 feet or more. It is also desirable to steer the apparatus that can provide such an underground tunnel.
It is therefore desirable to provide a horizontal drilling system (HDS) that can reach out to very long distances of up to 25,000 feet and more in favorable conditions. However, when drilling at horizontal distances of up to 25,000 feet and more, frictional forces and push forces become very large and result in failure by buckling and/or joint failure of the drillstring. The long drilling distances also require steerability of the drillstring to accomplish both reasonable accuracy and to navigate down and under an obstacle and then up again, for example. To provide such a system, it is necessary to minimize the friction resulting from the drillstring and drillhead. Accordingly, a hollow, continuously rotating drillstring (to reduce torsion and push forces) with constant inside diameter (for pigging capability) and constant outside diameter (for reducing friction between the drillstring and the bored tunnel) is preferred. Water jet cutting (to minimize push forces and add tension to overcome buckling) and using the drillstring as a conduit for supplying pressurized drilling fluid are also preferred.
Previous systems for steering (deviating) a drillstring are inadequate to operate under these parameters and are themeselves unable to accomplish these objectives.
One jetting technique for deviating a well from vertical includes orientating a large jet at the downhole end and towards the desired direction of deviation, initiating pumping to erode the hole in that direction, applying a high bit weight and then reciprocating the drillstring. After making a few feet, the hole is conventionaly drilled for about 20 feet and the procedure is repeated until the desired angle is obtained. This method, however, requires the drillstring to be completely non-rotating during the procedure. Other well known methods for deviating a well include a bent sub with a downhole mud motor; employing a whipstick; and using a rebal tool.
U.S. Pat. No. 4,930,586 to Turin et al, dated Jun. 5, 1990 discloses a fluid jet method and apparatus that uses poppet valves to control the discharge of a portion of the drilling fluid in radical directions forming steering jets.
U.S. Pat. Nos. 4,714,118; 4,821,815 and 4,856,600 to Baker et al discloses a fluid jet apparatus and technique that utilize a forward facing, off-axis high pressure rotating jet that is pushed through the soil. The boring device is steered by modulating the rotational speed of the off axis jet and/or by modulating the direction of rotation to cause the boring device to deviate.
Still another device in U.S. Pat. No. 5,148,880 to Lee et al, discloses a downhole tool with a fluid discharge nozzle parallel to the centerline axis of the tool and a blade for directing the fluid exiting the nozzle to an acute angle relative to the drillstring thereby cutting an elongate bore.
However, all these devices are inadequate for drilling long, horizontal bores of distance of up to 25,000 feet and more. Some require the drillstring to be stopped to orientate a cutting jet in the desired direction of deviation. Others require the drillstring to be removed from the hole to install a device to physically force the drillhead in a given direction. Some only permit one deviation, for example, from vertical to horizontal.
It is therefore an object of the present invention to provide an apparatus for boring a continuous underground tunnel either straight ahead (on axis) or deviating to the side (off axis).
It is another object of the present invention to provide and apparatus for boring a continuous underground tunnel that may be used with a hollow, continuously rotating, pushed drillstring.
It is a further object of the present invention to provide an apparatus to drill a continuous underground tunnel by means of high pressure fluid jets.
It is another object of the present invention to provide an apparatus for boring a continuous underground tunnel to distance out to 25,000 feet and more.